Methicillin-resistant Staphylococcus aureus and extended-spectrum and AmpC β-lactamase-producing Escherichia coli in broilers and in people living and/or working on organic broiler farms

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Highlights

  • MRSA was not detected in broiler and human samples on organic farms.

  • All organic farms were ESBL/AmpC-positive; ≥80% of broilers and 18.5% of humans.

  • Within-flock prevalence was lower at slaughter age (80%) than at 34 days (94.3%).

  • Carriage of ESBL/AmpC-E. coli among humans can be both persistent and intermittent.

Abstract

The aim of this study was to estimate the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) and extended-spectrum and AmpC β-lactamase (ESBL/AmpC)-producing Escherichia coli among broilers, and humans living and/or working on organic broiler farms; further characterise isolates; and compare these results with those from conventional farms.

In the Netherlands, only 9 certified organic broiler farms were present. On 8 of these farms, 60 throat swabs and 20 cloacal swabs were taken per farm for MRSA and ESBL/AmpC-E. coli detection, respectively, at an average age of both 34 (T1) and 68 (T2) days. Faecal swabs and questionnaires were returned by 27 out of 36 humans. For selected ESBL/AmpC-producing E. coli isolates, phylogenetic groups, β-lactamase genes, plasmid families, and sequence types were determined.

MRSA was not detected in broiler and human samples. ESBL/AmpC-producing E. coli were isolated from broilers on 7/8 farms at T1 and on all farms at T2. Furthermore, 3 farmers at T1, and 2 farmers and 1 family member at T2 were positive. Genes found in broilers and humans were almost exclusively blaCTX-M-1 and blaCMY-2. Given the high overall human ESBL/AmpC-prevalence (18.5%), which is similar to conventional farms, contact with live broilers is assumed a risk factor for carriage. Farm and sample-level prevalence at T1 are consistent with those from conventional farms. At T2, just before slaughter, sample-level prevalence of ESBL/AmpC-E. coli appears to have decreased (94.3% vs. 80%), which could have important consequences for contamination of retail meat.

Introduction

Human infections with methicillin-resistant Staphylococcus aureus (MRSA), and extended-spectrum and AmpC β-lactamase (ESBL/AmpC)-producing Escherichia coli have both been associated with reservoirs in livestock (van Loo et al., 2007, Carattoli, 2008). This raises a public health concern as transmission could occur between animals and humans. Livestock-associated (LA)-MRSA and ESBL/AmpC-producing E. coli have been found in broilers, and in individuals working and/or living on conventional Dutch broiler farms (Dierikx et al., 2013, Geenen et al., 2013, Huijbers et al., 2014). The prevalences of MRSA and ESBL/AmpC-producing E. coli are higher in humans on these farms than in the community (Bode et al., 2011, Geenen et al., 2013, Huijbers et al., 2013, Huijbers et al., 2014), and contact with live broilers has been identified as a risk factor for human carriage (Mulders et al., 2010, Huijbers et al., 2014).

In comparison to conventional farms, organic broiler farms have lower flock densities, different breeds, restrictions in antimicrobial use, availability of outdoor areas, and later slaughter age. These factors could lead to a lower prevalence of MRSA and ESBL/AmpC-producing E. coli among broilers on organic compared to conventional farms, and might also affect carriage of humans. There are currently no studies investigating carriage of MRSA and ESBL/AmpC-producing E. coli among humans and broilers on organic farms. The aim of this study was to estimate the prevalence of MRSA and ESBL/AmpC-producing E. coli among broilers, and humans living and/or working on organic broiler farms; further characterise isolates from humans and broilers; and compare these results with those from conventional farms.

Section snippets

Study population

From October 2011 to April 2012 a prevalence study for MRSA and ESBL/AmpC-producing E. coli was conducted on 8 out of 9 certified organic broiler farms in the Netherlands. Certified organic broiler farms are those that comply with legal regulations laid down by the European Commission. Chapter 2 of Commission Regulation No. 889/2008 describes production rules for different livestock species, including broilers (EC, 2008). Participating farms had a median of 1.5 broiler houses (range 1–22) and

Descriptive statistics

In total, 27 out of 36 individuals agreed to participate. These participants included 9 farmers, 16 family members, and two employees. Per farm, this ranged from two to seven individuals, with an average age of 40.6 years (range 4–76 years).

MRSA-carriage among broilers and humans

MRSA was not detected in all 80 pooled throat swabs and 120 environmental wipes, so all farms were classified MRSA-negative. The prevalence of positive organic farms (0/8) was not statistically different (P = 1.0) from conventional farms (4/50; Geenen et al.,

Conclusion

MRSA was not detected in broilers or humans on Dutch organic broiler farms. In contrast, ESBL/AmpC-producing E. coli were detected in broilers on all farms, with a prevalence of ≥80% at the sample-level, and in 18.5% of humans. Given the higher prevalence of ESBL/AmpC-producing E. coli among humans living and/or working on organic farms compared to the general Dutch population and similarity to the prevalence in humans on conventional farms, contact with live broilers could also be a risk

Conflict of interest

None declared.

Acknowledgements

This work was financially supported by the Netherlands Food and Consumer Product Authority (NVWA) (grant number V330091). We would like to thank all farmers, their family members and employees for participating in this study.

References (21)

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